1. Field of the Invention
The invention relates to a plant for transferring a gas into a liquid, especially for transferring, into such a liquid, carbon dioxide (for carbonation), oxygen (for oxygenation), ozone (for ozonation) or nitrogen, for example for the purpose of displacing a gas already dissolved in the liquid. The term xe2x80x9cgasxe2x80x9d is understood to mean a fluid which is in the gaseous state under normal temperature and pressure conditions but which, under the operating conditions, may either be in the gaseous state or in the liquid state when it is introduced into the liquid proper.
2. Description of the Related Art
In general, a mass of liquid, which initially contains no gas or contains little gas and the free surface of which is in contact with a volume of gas, receives a transfer of a portion of the gas into the liquid and the combination tends towards a liquid-gas distribution in stable equilibrium. It may be demonstrated that the mass M of gas that can be transferred into a certain volume of liquid is proportional to the difference D between the saturation concentration and the actual concentration, to the area A of the liquid-gas interface, to the time t and to a surface transfer coefficient f. It will be noted that the difference D varies over time, becoming zero.
If, for the purpose of reducing the duration of the transfer operation, it is desired to increase the area of the interface A between the liquid and the gas, all other things remaining equal, this results in relatively large transfer plants.
The object of the invention is to remedy this drawback and, for this purpose, relates to a plant for transferring a gas in the gaseous state or in the liquid state into a liquid, characterized in that it comprises a liquid circuit in at least part of which the liquid flows under pressure, a gas circuit in at least part of which the gas under pressure flows and which includes, at the outlet, a device for injecting gas in the gaseous state or in the liquid state under pressure and emerging in that part of the liquid circuit in which the liquid flows under pressure, the liquid circuit including a chamber for mixing the gas with the liquid, the said chamber being located downstream of the gas injection device and having an outlet connected to the overhead of a buffer tank located downstream of the mixing chamber, in order to introduce into the buffer tank, in the form of liquid droplets or streams, liquid with which gas is mixed, and means for withdrawing, from the buffer tank, liquid with which gas is mixed.
By virtue of these characteristics, the plant is very efficient and allows rapid transfer without occupying a large space; in addition, it allows the amount of gas dissolved in the liquid to be very accurately adjusted.
The plant may furthermore have one or more of the following characteristics:
it includes means for adjusting the pressure of the overhead of the buffer tank;
it includes means for adjusting the pressure of the overhead of the buffer tank according to the temperature of the liquid;
the adjustment means comprise means for measuring the said pressure and for comparing it with a set pressure, means for discharging gas from the buffer tank if the measured pressure is above the set pressure and means for admitting gas into the buffer tank if the measured pressure is below the set pressure;
the said admission of gas is done into the overhead of the buffer tank;
the gas is carbon dioxide, for example carbon dioxide filtered and sterilized for food applications;
the gas is nitrogen, oxygen or ozone;
the liquid is an aqueous liquid;
the gas is introduced into the liquid circuit in the gaseous state and the injection device comprises an injection apparatus slaved to the transfer pump so that the gas flow is interrupted if the pump stops, this apparatus feeding an outlet injector which emerges in the liquid circuit;
the gas is introduced into the liquid circuit while itself being in the liquid state, and the injection device comprises an expansion and control valve feeding an outlet injector which emerges in the liquid circuit;
the mixing chamber is a device consisting of a succession of tubes forming a coil, such as a tube reactor;
the mixing chamber is an in-line static mixer;
the means for adjusting the pressure in the overhead of the tank have a set pressure which varies according to the temperature of the liquid;
the means for adjusting the pressure in the overhead of the tank comprise an expansion valve, the inlet of which is connected to the gas circuit and the outlet of which is connected to the overhead of the tank.